Rhabdomyosarcoma in a prehensile-tailed porcupine

A captive 4-y-old female prehensile-tailed porcupine (Coendou prehensilis) had quill loss caudal to the right ear associated with an ~1-2-cm palpable mass. The mass was surgically debulked and diagnosed histologically as a poorly differentiated neoplasm. Ten days after surgery, the porcupine became anorectic and severely ataxic with a moderate left-sided head tilt and was euthanized and submitted for postmortem examination. Deep to the surgical site was a 7 × 3 × 0.5-cm amorphous, tan, soft, irregularly shaped mass that encircled the right ear canal and invaded skeletal muscle and the right tympanic bulla. Histologically, the densely cellular, infiltrative and destructive, unencapsulated neoplasm was comprised of interlacing bundles, streams, and herringbone arrangements of spindle cells supported by scant fine stroma. Neoplastic cells invaded muscle and the bone of the tympanic bulla. Neoplastic cells had cytoplasmic immunolabeling for myogenin, myoD1, vimentin, smooth muscle actin, and desmin, and were immunonegative for S100 and CD31. The mass was diagnosed as a rhabdomyosarcoma. To our knowledge, rhabdomyosarcoma has not been reported previously in any porcupine species.